Why does synchronzing a custom repository in Satellite 6 fail with error "Treeinfo file should have INI format"?

Issue

• Attempting to synchronize a custom repository fails with error "Treeinfo file should have INI format":

---
pulp_tasks:
- pulp_href: "/pulp/api/v3/tasks/c0529750-cf7c-422d-bfa7-f30f75de22b2/"
  pulp_created: '2023-09-14T13:07:04.125+00:00'
  state: failed
  name: pulp_rpm.app.tasks.synchronizing.synchronize
  logging_cid: af640767-d9bb-4e3e-ac08-471ffffb9883
  started_at: '2023-09-14T13:07:04.165+00:00'
  finished_at: '2023-09-14T13:07:04.217+00:00'
  error:
    traceback: !ruby/string:Sequel::SQL::Blob |2
        File "/usr/lib/python3.9/site-packages/pulpcore/tasking/pulpcore_worker.py", line 410, in _perform_task
          result = func(*args, **kwargs)
        File "/usr/lib/python3.9/site-packages/pulp_rpm/app/tasks/synchronizing.py", line 497, in synchronize
          treeinfo = get_treeinfo_data(remote, remote_url)
        File "/usr/lib/python3.9/site-packages/pulp_rpm/app/tasks/synchronizing.py", line 439, in get_treeinfo_data
          treeinfo.load(f=result.path)
        File "/usr/lib/python3.9/site-packages/pulp_rpm/app/kickstart/treeinfo.py", line 28, in load
          raise TypeError(_("Treeinfo file should have INI format"))
    description: Treeinfo file should have INI format
  worker: "/pulp/api/v3/workers/e098c6e0-f335-4ea6-b87a-fef7cb70d40f/"
  child_tasks: []
  progress_reports: []
  created_resources: []
  reserved_resources_record:
  - "/pulp/api/v3/repositories/rpm/rpm/1ff5f07e-028d-4253-98fd-c93c15795471/"
  - shared:/pulp/api/v3/remotes/rpm/rpm/4c5ed8a2-f382-48b6-9064-4f81bf592b9c/
create_version: true
task_groups: []